Process of treating sulphite waste



United States Patent No Drawing. Application March 5, 1956 Serial No.569,259

4 Claims. (Cl. 204-131) This invention relates to a process of treatingsulphite waste and this application is a continuation-in-part of myprior application Serial Number 304,642, filed August 15, 1952, nowabandoned.

An object of this invention is to provide a new and useful electrolyticprocess of recovering, separating and extracting lignin and itsassociated products from the material known as sulphite waste whichresults from reactions undergone in the sulphite process of paper pulpmanufacture.

Another object of this invention is to separate and remove lignin or itsmodified form from sulphite waste in the form of calciumligno-sulphonate and anode-metal ligno-sulphonate.

A further object of this invention is to convert lignin and itsassociated products into a physical form and condition capable of beingeasily removed from the sulphite waste solution and successfullyrecovered as a tangible and valuable product and to render the sulphitewaste liquid innocuous so that it can be safely discharged into streamsand like surface waters.

A further object is to provide a chemical reduction process suitable tohydrogenate or deoxidize the lignin component of calcium ligninsulphonate as well as to saturate its base metal component by treatingthe sulphite waste as an electrolytic bath wherein a metal of highelectromotive force is dissolved at the positive pole and hydrogen at anovervoltage on zinc or other metal of similar characteristics is evolvedat the negative pole,

the metal and hydrogen ions both being highly chemically reactant toeffect hydrogenation of the lignin and also to reduce the valence of themetal component.

Other objects of the invention will be apparent from the followingdescription,

Lignin and its associated products resulting from the sulphite processof extraction are quite susceptible to reduction, either byhydrogenation or by deoxidation. It is hereby proposed to employ anelectrolytic process wherein both electrodes are in intimate contactwith the sulphite waste products and to use active reducing agents, suchas electropositive anodes ofv metal classed above hydrogen, which israted zero for sealing purposes in the electromotive force seriesactivity lists. As an illustrative listing of electromotive force seriesof elements reference is made to page 1575 of the Handbook of Chemistryand Physics, 34th edition, 1952-1953, published by Chemical RubberCompany of Cleveland, Ohio. Any metal rated above hydrogen in this listmay be used for anode purposes, except the pure forms of the alkalimetal group, namely sodium, potassium, lithium and rubidium, whichoxidize in air too readily and are too violent in contact with water.Iron, magnesium, aluminum, zinc and their alloys have been found to bepracticable anode metals. The cathodes may be of any metal or alloy ofmetals, either electropositive or electronegative, except the metalsjust hereinbefore mentioned as oxidizing too readily in air and beingtoo violent in water. One satisfactory cathode metal is zinc, which hasa high iicontact with and immersed in the same body of sulphite "icehydrogen over-voltage and is highly effective in the re duction.

The reducing action of the above mentioned metals and nascenthydrogenapplies to ionized and un-ionized substances in solution,miscible components and solids in suspension,'thus affecting all of thematerials which are subject to reduction In practice, this process ofreduction occurs before any coagulation takes place. The choice ofmetals used as anodes will be governed by several considerations amongwhich are cost of the metal, specific ability to coagulate thesubstances being treated and ability to produce coagulations having adesired base-element including the exclusion from coagulations ofelements whichwould be objectionable in the recovered product. Alloys ofthe metals used for anode purposes offer certain advantages, such as awider range ofcoagulation and aiding in the solution of the metal. Forinstance, it has been found carbon steel dissolves more readily thanwrought iron.

a By way of example, the treatment ofthe sulphite waste may be batchtreatment in a .vat or like receptacle or continuous flow treatment in atrough or conduit through whichthe-sulphite waste moves progressively.In either instance one or-more anodes formed of metal high in theelectromotive force series, such as iron, aluminum, magnesium,-zinc oralloys of these and other electropositive metals, .and one or morehydrogen evolving cathodes of metals, such as zinc, iron, copper,aluminum or the like, are positioned so that they will be in directwaste. Different metals or alloys may be used as anodes in the same vatorconduit. The sulphite Waste usually comes from the mill at atemperature of about degrees Fahrenheit and I prefer to start thetreatment at about this temperature because electrical resistance isless at higher temperatures. successfully carried out at lowertemperaturesincluding normal cold water temperature. As an initial stepin the treatment the sulphite waste is .alkalized sufficiently toproduce a visible discoloration and a slight precipitatev by adding asmall amount of alkalizing agent such as KOH, NaOH, NH OH or CaOH. Thevisible discoloration and precipitate will occur at a pH ranging from7.0 to 7.5 and both will disappear later under the reducing action. Theconcentration of the sulphite waste at the start is usually abouttwelvepercent. This concentration is not critical and it may vary due todifferent mill procedures and due, sometimes, to the addition of fiberwash water. The-waste solution is placed or led between the opposedelectrodes which have at least two volts of direct current applied witha current density of approximately thirtyv six amperes per square foot.About fifteen minutes elapses before any apparentchange takes place,after which frothing and coagulation commence. The time of treatment isapproximately one hour, depending on the Some of the coagulation adheresinitial concentration. to the anode, some settles and some rises in thefroth, all of which can be collected. The adherence to the anode varieswith different metals, with iron it is considerable and needs to bescraped off or a reversal of polarity will cause it to drop off. Withaluminum very little adherence occurs. The amount of metal dissolved atthe anode is definitely an electrochemical equivalent. In practice itrequires about two grams of iron to obtain twenty grams of dehydratedcoagulate. About one gram of aluminum will obtain the same amount ofdehydrated coagulate. The dissolution of the anode requires its frequentreplacement.

The sulphite waste is a good electrical conductor although a trace of anactive ionizing salt, such as sodium chloride or sodium sulphate may beadded to increase the anode dissolution rate. The visible indicationswhen However the treatment may be.

the solids have been completely extracted are several;

when using aluminum as an anode the froth at first is grayish andbecomes white toward the end; when using iron the anode emits oxygen atthe end; when using aluminum the normal amber color of the sulphitewaste solution disappears toward the end.

The anode ions can not enter the solution without first engaging acidsor oxygen, which involves reduction, primarily, as well as a reductionin the valence of the initial metal component. The oxidation productsand the reduced valence combinations set up coagulation, depend ing alsoon the particular anode metal used. By using a sectional running troughmethod in which the sulphite waste is passed successively from onetrough to another various degrees and modifications of lignin and itsrelated substances are recovered due to their different tendencies tobecome insoluble in sequence. The principal coagulations are two or morebasic compounds; calcium lignosulphonate and anode-metalligno-sulphonate. Other ligneous compounds may result, depending on thestate of the lignin in the sulphite waste.

Obviously changes in this invention may be made within the scope of thefollowing claims.

I claim:

1. The process of treating lignin and its associated products which haveresulted from the reactions undergone in the sulphite method of paperpulp manufacture for the purpose of deoxidizing such products, whichcomprises adding an alkali in suflicient quantity to the sulphite wastesolution to cause a visible discolored suspension and a slightprecipitate; and then subjecting the alkalined sulphite waste toelectrolysis at not less than two volts between a positive electrode ofhigh electromotive force and a hydrogen evolving negative electrode in asingle compartment in which both electrodes are in direct and intimatecontact with the sulphite waste products, whereby the oxygenconcentrated at the positive electrode under electrolytic pressure isneutralized by the ionic products of the dissolving positive electrodeand the nascent hydrogen ionic products emanating from the negativeelectrode thereby effecting a reduction in the condition of the ligninand its associated products.

2. The process of treating lignin and its associated products which haveresulted from the reactions undergone in the sulphite method of paperpulp manufacture for the purpose of deoxidizing such products, whichcomprises adding an alkali in suflicient quantity to the sulphite wastesolution to alkalize the same to a pH of 7.0 to 7.5 and cause a visiblediscolored suspension and a slight precipitate; and then subjecting. thealkalined sulphite waste to electrolysis at not less than two voltsbetween a positive electrode comprising a metal higher than hydrogen inthe electromotive force series and a hydrogen evolving negativeelectrode in a single compartment in which both electrodes are in directand intimate contact with the sulphite waste products, whereby theoxygen and acids concentrated at the positive electrode underelectrolytic pressure are neutralized by the ionic products of thedissolving positive electrode and the nascent hydrogen ionic productsemanating from the negative electrode thereby efiecting a reduction inthe condition of the lignin and its associated products.

3. The process of hydrogenating and saturating lignin and its associatedproducts which have resulted from reactions undergone in the sulphitemethod of paper pulp manufacture to render them insoluble and separableand capable of recovery, which comprises adding an alkali in sufficientquantity to the sulphite waste solution to alkalize the same to a pH inthe order of 7.0 to 7.5 and cause a visible discolored suspension and aslight precipitate; and then subjecting the alkalined waste solution toelectrolysis at not less than two volts and at a current density ofapproximately thirty six amperes per square foot of electrode surfacebetween a positive electrode comprising a metal higher than hydrogen inthe electromotive force series and a hydrogen evolving negativeelectrode in a single compartment in which both electrodes are in directand intimate contact with the sulphite waste products, whereby theoxygen and acids concentrated at the positive electrode underelectrolytic pressure are neutralized and saturated by the ions of thedissolving positive electrode and the products resulting frombydrogenation and whereby the hydrogenated products and basicallysaturated salt products are coagulated in the alkalined solution.

4. The process of deoxidizing ligno-sulphonic acid which is compoundedwith a base element and dissolved in the water solution which hasresulted from reactions undergone in the sulphite process of paper pulpmanufacture for the purpose of rendering said compound insoluble andseparable from the water solution and to reduce the ligno-sulphonicacid, comprising adding an alkali in limited quantity to the solution toalkalize said solution to a pH in the order of 7.0 to 7.5 and causevisible discoloration and produce a slight but non-permanentprecipitate; and then subjecting the alkalized solution to directcurrent electrolysis between a positive electrode formed of a metalhaving a higher rating than hydrogen in the electromotive force seriesand a hydrogen evolving negative electrode at not less than two voltsand at a current density of approximately thirty six amperes per squarefoot of electrode surface with the electrodes and solution in a singlecompartment and with both electrodes in direct and intimate contact withthe solution, whereby oxygen and acids concentrated at the positiveelectrode under electrolytic pressure are neutralized by ions of thedissolving positive electrode and the products resulting fromhydrogenation occurring at the negative electrode and whereby thehydrogenated products and basically saturated salt products arecoagulated in the said alkalined solution, said coagulated mattercontaining anode metal and hydrogen in combination with the originalbase element.

References-Cited in the file of this patent UNITED STATES PATENTS

1. THE PROCESS OF TREATING LIGNIN AND ITS ASSOCIATED PRODUCTS WHICH HAVERESULTED FROM THE REACTIONS UNDERGONE IN THE SULPHITE METHOD OF PAPERPULP MANUFACTURE FOR THE PERPOSE OF DEOXIDIZING SUCH PRODUCTS, WHICHCOMPRISES ADDING AN ALKALI IN SUFFICIENT QUANTITY TO THE SULPHITE WASTESOLUTION TO CAUSE A VISIBLE DISCOLORED SUSPENSION AND A SLIGHTPRECIPITATE, AND THEN SUBJECTING THE ALKALINED SULPHITE WASTE TOELECTROLYSIS AT NOT LESS THAN TWO VOLTS BETWEEN A POSITIVE ELECTRODE OFHIGH ELECTROMOTIVE FORCE AND A HYDROGEN EVOLVING NEGATIVE ELECTRODE IN ASINGLE COMPARTMENT IN WHICH BOTH ELECTRODES ARE IN DIRECT AND INTIMATECONTACT WITH THE SULPHITE WASTE PRODUCTS, WHEREBY THE OXYGENCONCENTRATED AT THE POSITIVE ELECTRODE UNDER ELECTROLYTIC PRESSURE ISNEUTRALIZED BY THE IONIC PRODUCTS OF THE DISSOLVING POSITIVE ELECTRODEAND THE NASCENT HYDROGEN IONIC PRODUCTS EMANATING FROM THE NEGATIVEELECTRODE THEREBY EFFECTING A REDUCTION IN THE CONDITION OF THE LIGNINAND ITS ASSOCIATED PRODUCTS.